Vol. 10: 79–88, 2018 AQUACULTURE ENVIRONMENT INTERACTIONS Published February 19 https://doi.org/10.3354/aei00255 Aquacult Environ Interact OPENPEN FEATURE ARTICLE ACCESSCCESS Adding value to ragworms (Hediste diversicolor) through the bioremediation of a super-intensive marine fish farm Bruna Marques1, Ana Isabel Lillebø1, Fernando Ricardo1, Cláudia Nunes2,3, Manuel A. Coimbra3, Ricardo Calado1,* 1Department of Biology & CESAM & ECOMARE, 2CICECO − Aveiro Institute of Materials, and 3Department of Chemistry & QOPNA, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal ABSTRACT: The aim of this study was to evaluate the potential added value of Hediste diversicolor, cultured for 5 mo in sand bed tanks supplied with effluent wa- ter from a super-intensive marine fish farm, by com- paring their fatty acid (FA) profile with that of wild specimens. The polychaetes showed an approximately 35-fold increase in biomass during the experimental period and their FA profile was significantly different from that of wild specimens. In cultivated specimens, the most abundant FA class was that of highly unsatu- rated FA (HUFA), with eicosapentaenoic acid (EPA, 20:5n-3) being the best represented. Similar percent- age (SIMPER) analysis showed an average 20.2% dis- similarity between the FA profile of wild and culti- vated specimens, supporting the view that the culture system employed enables the recovery of high value Ragworms (Hediste diversicolor) on sand filters of a super- nutrients (e.g. EPA and docosahexaenoic acid [DHA, intensive brackish-water fish farm, cultured using the 22:6n-3]) from fish feeds into the tissues of H. diversi- farm’s organic-rich effluent and displaying a greater con- color that would otherwise be lost from the production tent of docosahexaenoic acid (DHA, 22:6n-3) than wild environment. While the nutritional value of wild rag- conspecifics. worms is well established in marine aquaculture Photo: Bruna Marques, Universidade de Aveiro (namely for broodstock maturation diets), the higher level of DHA displayed by the specimens produced under the proposed culture system may grant them a premium market value. where’ (Martins et al. 2010). The principles behind RAS promote the treatment and reuse of culture wa- KEY WORDS: Integrated multi-trophic aquaculture · ter, with 10% or less of the total water volumes hav- IMTA · Polychaete-assisted sand filters · Fatty acids ing to be replaced per day (Hutchinson et al. 2004, van Rijn et al. 2006). However, one of the constraints impairing the expansion of these production systems (in a closed or semi-closed operation) is the challenge INTRODUCTION associated with the load of organic-rich suspended particulate matter (POM), dissolved orga nic matter Recirculating aquaculture systems (RAS) are cur- (DOM) and nutrients in dissolved inorganic form (ni- rently considered one of the paradigms of the Blue trogen, N, and phosphorus, P) present in its effluent Revolution, as they allow people to ‘grow fish any- (Schneider et al. 2005, Marques et al. 2017). © The authors 2018. Open Access under Creative Commons by *Corresponding author: [email protected] Attribution Licence. Use, distribution and reproduction are un - restricted. Authors and original publication must be credited. Publisher: Inter-Research · www.int-res.com 80 Aquacult Environ Interact 10: 79–88, 2018 A number of integrated multi-trophic aquaculture and they are also able to scavenge and actively prey (IMTA) systems have been developed in order to re - on other organisms (including conspecifics) (Luis & duce the nutrient load present in the effluents pro- Passos 1995, Fidalgo e Costa et al. 2000, Bischoff et duced when growing finfish or shrimp. In other al. 2009). The interactions with its environment show words, IMTA combines the integrated culture of fed an efficient adaptation to a variation of environmen- target species (e.g. finfish/shrimp) with that of ex- tal parameters such as salinity, temperature and dis- trac tive species that use particulate or dissolved solved oxygen (Smith 1964, Fritzsche & von Oertzen orga nic matter (e.g. shellfish/herbivorous fish) or dis- 1995, Murray et al. 2017). Polychaetes also play an solved inorganic nutrients (e.g. seaweed/halophytes) important ecological role in the marine environment, generated through the excretion products of fed spe- as they are major contributors to the resuspension of cies and uneaten feed (Schneider et al. 2005, Chopin organic matter via bioturbation (Würzberg et al. et al. 2008, Alexander et al. 2015). Overall, this envi- 2011), a feature of great relevance for their potential ronmentally friendly approach aims to address the use in IMTA. Indeed, some studies have already im pacts commonly associated with conventional highlighted how polychaetes can be successfully aqua culture, such as nutrient loading and sedimen- employed in the bioremediation of aquaculture efflu- tation (Schneider et al. 2005, Barrington et al. 2009). ents under an IMTA framework (Palmer 2010, Fang In this way, promoting IMTA practices may help to et al. 2017). overcome the current bottlenecks faced by enter- The nutritional value of ragworms is well estab- prises operating RAS, as the nutrient-rich effluents lished in marine aquaculture, with these organisms that they generate may be used to culture additional being a highly valued item in marine finfish and species. While on one side this approach allows the shrimp maturation diets (Olive 1999, Techaprem- nutrient load issue to be addressed from a biomitiga- preecha et al. 2011, Santos et al. 2016). One of the tion perspective, through the incorporation of nutri- main reasons for their popularity is their fatty acid ents in extractive species biomass, it also opens up (FA) profile, namely the levels they display of impor- the opportunity of adding new cash-crops to the pro- tant polyunsaturated FA (PUFA) (Brown et al. 2011, duction model through the valorization of those Santos et al. 2016). Some polychaete species, includ- extractive species (Chopin et al. 2008, Alexander et ing H. diversicolor, are able to biosynthesize PUFA, al. 2015). such as 20:5n-3 eicosapentaenoic acid (EPA) and The polychaete Hediste diversicolor (O.F. Müller, 22:6n-3 docosahexaenoic acid (DHA), which are 1776), popularly known as ragworm, is a candidate known to be essential for marine finfish and shrimp species for land-based IMTA systems, as it can effi- (Olive 1999, Fidalgo e Costa et al. 2000). ciently recycle particulate organic nutrients present In order to evaluate the potential valorization of in fish farm effluents (Scaps 2002, Bischoff et al. 2009, H. diversicolor cultured in sand bed tanks supplied Santos et al. 2016). This polychaete is a burrowing with effluent water from a super-intensive marine species that inhabits the soft bottoms of shallow mar- fish farm, their fatty acid profile was determined and ine and brackish waters environments, generally in compared with that of wild specimens. The experi- sediments with high organic contents, in the North mental procedure aimed to test (1) whether ragworm temperate zone of European and North American FA profiles depend on food source, by comparing Atlantic coasts (Scaps 2002, Lillebø et al. 2012). H. cultured and wild specimens, and (2) whether the FA diversicolor exhibits a ‘bentho-pelagic life cycle’ profiles of ragworms cultured in sand bed tanks sup- (Scaps 2002, Nesto et al. 2012). It is one of the rare plied with RAS effluent are size-dependent, by com- Nereid species which remain atokous throughout paring small, medium and large ragworms. their lifespan, contrasting with some other Nereids which undergo a metamorphosis to a typical epitok- ous heteronereid form (Scaps 2002, Breton et al. MATERIALS AND METHODS 2003, Aberson et al. 2011). During reproduction, the female incubates the eggs for a period of 10 to 14 d Experimental set-up inside the gallery, and dies soon afterwards. In this way, the direct or brooded larval development per- Effluent originating from a super intensive RAS mits a greater flexibility in the level of development system farming Senegalese sole Solea senegalensis of the released offspring (Aberson et al. 2011). The was pumped from a settling basin to a bio-block feeding modes of this polychaete are diversified, tower system, in order to allow the effluent water to ranging from surface deposit to suspension feeding, trickle and increase its oxygen levels before reaching Marques et al.: Ragworm cultivation and added value 81 the header tank reservoir. In this header tank, the (20). Subsequently, all sampled specimens were effluent was strongly aerated and set to flow in paral- separated into 3 pre-established size classes (small lel into 6 experimental sand bed tanks. Each of these <30 mm, medium 30 to 50 mm and large >50 mm). At tanks had an approximate volume of 1 m3 and a sur- the beginning of the experiment, triplicate samples of face area of 1 m2. The bottom of each tank was cov- WP (all from the large class) that were used to stock ered by 200 mm of sand (1 to 2 mm grain size substra- the tanks, were left to depurate overnight under tum) beneath which a draining pipe allowed the identical conditions as those previously described. effluent water to percolate through the sand bed. After depuration, wild polychaetes and those origi- Each tank was equipped with 2 outlets, one that reg- nating from the sand bed tanks were freeze-dried ulated the water level inside the tank and allowed and stored at −80°C for subsequent FA analysis. the water to drain and another one that was set to prevent the tank from overflowing in case the sand bed became clogged and impaired water percola- Sampling of potential nutrient sources of POM for tion. Sand bed tanks were placed in parallel and sup- FA analysis plied with aerated RAS effluent water by gravity at a flow of 180 l h−1. All tanks were equipped with a To perform the FA characterization of all potential 0.8 m diameter ring of aeration hose supplying com- nutrient sources available to the ragworms stocked in pressed air (see Marques et al.